Question: What is the condition for constructive interference of two waves?

Options:

1. Path difference is an odd multiple of half the wavelength
2. Path difference is an even multiple of the wavelength
3. Waves are out of phase
4. Waves are in phase

Correct Answer: Path difference is an even multiple of the wavelength

Solution:

Constructive interference occurs when the path difference between two waves is an even multiple of the wavelength.